1. Field of the Invention
The present invention relates to a planar light-emitting device that illuminates a liquid crystal display panel or the like. The present invention also relates to a liquid crystal display apparatus using such a planar light-emitting device.
2. Description of the Related Arts
Liquid crystal display apparatuses for image display are widely used as the large-sized displays of flat-screen television systems and monitors, etc. These liquid crystal display apparatuses employ a backlight unit that applies illuminating light to a liquid crystal display panel from the back to enhance the luminance of the display screen. One type of such a backlight unit, for example, has a lightguide plate and a light source comprising, for example, light-emitting diodes (LEDs) disposed adjacent to the peripheral side surface of the lightguide plate. The lightguide plate guides light from the light source and emits the guided light from the whole of a light exiting surface directed toward a liquid crystal display panel. There is another type of backlight unit known as a direct light type that uses no lightguide plate. In the direct light type backlight unit, a plurality of light sources are installed directly below a liquid crystal display panel with a sheet-shaped light-diffusing element, e.g. a diffusing sheet, interposed between the panel and the light sources, and each light source illuminates the liquid crystal display panel through the sheet-shaped light-diffusing element.
Recently, as liquid crystal television systems increase in size, the demand for reduction in weight and thickness of the television systems has been becoming stronger. In this regard, there are some problems to be solved. A backlight unit using a lightguide plate needs to install a large-sized lightguide plate or a plurality of lightguide plates in juxtaposed relation, resulting in an increase in weight. The direct light type backlight unit, which uses no lightguide plate, allows a weight reduction corresponding to the weight of a lightguide plate that would otherwise be used, but needs to set a wide spacing between the light sources and the sheet-shaped light-diffusing element in order to prevent the occurrence of luminance unevenness of illuminating light applied to the liquid crystal display panel.
Japanese Patent Application Publication No. 2007-157451, for example, proposes a backlight unit provided with sheet-shaped light-diffusing element support members in the shape of support posts to support a sheet-shaped light-diffusing element while ensuring a required spacing between the sheet-shaped light-diffusing element and light sources. In this backlight unit, the sheet-shaped light-diffusing element is supported by the upper ends of the support members to separate the light-diffusing element from the light sources. In this related art, however, a thin sheet-shaped light-diffusing element is supported by the tapered ends of the support members. Therefore, the thin light-diffusing element is deflected undesirably. To cope with this problem, a thick sheet-shaped light-diffusing element may be used to suppress the deflection, which, however, would interfere with the reduction in overall thickness and weight of the backlight unit.